Turbo-molecular vacuum pump



June 23, 1964 H. GARNIER ETAL 3,138,318

TURBO-MOLECULAR vAcuun/L PUMP Filed April 20, 1962 l-NVE/Vks H. L.@ARN/1:@ l.. Rubel A). E MARC/44 L Bv Marsan (1a/1 5ml/le Msou UnitedStates Patent O 3,138,318 TURBO-MOLECULAR VACUUM PUMP Henri LouisGarnier, Courbevoie, and Lonide Rubet and Raymond Hippolyte FirminMarchal, Paris, France, assignors to Societe Nationale dEtude et deConstruction de Moteurs dAviation, Paris, France, a company of FranceFiled Apr. 20, 1962, Ser. No. 189,021 Claims priority, applicationFrance May 15, 1961 1 Claim. (Cl. 2310-122) The present inventionderives from the principle of the turbo-compressor rotating at a highspeed, such as is currently used in aircraft. Experiments, which agreein every way with the theory, have established that a distinctly highercompression rate is obtained when the turbo-compressor operates in arareiied atmosphere.

The present invention utilises this knowledge in the eld of highvacuums.

In a vacuum pump, the cross-section of the blades is greatly simplifiedas compared with the cross-section of the blades normally used inturbo-compressors. In fact, the problems connected with flows in theviscous and turbulent conditions are no longer encountered in the caseof gases in a molecular condition. The various stages of the vacuum pumpare simply constituted by a series of thin discs which are alternatelyfixed and mobile and on the periphery of which the blades are arranged.

The present invention relates to a turbo-molecular vacuum pumpcharacterised in that the blades have a triangular cross-section andcomprise a sharp edge directed towards the chamber to be evacuated,whilst the opposite face to this edge is directed towards the dischargeside. In other words, each blade is in the form of truncated prismhaving a triangular base whose most acute dihedral angle is directedtowards the upstream side, i.e. in the direction of the high vacuum.Consequently, the face which is opposite this dihedral angle and whoseplane is perpendicular to the axis of rotation of the pump, is turned inthe direction of the preliminary vacuum.

This arrangement enables the gases diffused from the chamber to beevacuated to penetrate easily into the ducts which are bounded by theblades and which are wide open to these gases.

The following description with reference to the accompanying drawings,which are given by way of nonlirnitative example, will make it easy tounderstand how the invention can he carried into effect, the featuresbrought out either from the text or from the drawings being understoodto form part of the said invention.

FIG. 1 is an axial sectional View of a turbo-molecular vacuum pump.

FIG. 2 is a cross-section on II-II of FIG. 1.

FIG. 3 is a partial developed view of two successive blade systems,showing the basic feature of the present invention.

The pump shown in FIG. 1 is of a well-known and already old type, havingbeen proposed by Holweck as early as 1922. Suction is effected throughthe inlet E, in the median plane of the casing C of the pump, thevarious stages being arranged symmetrically with respect to the medianplane, and the outlets S at the two ends of the casing being connectedby a pipe T to the suction P of a forepump (not shown) which may be anordinary vacuum pump. The shaft A of the turbo-molecular pump can bedriven by a built-in motor. This shaft is fast with rotary discs Rseparated by fixed discs F, on the periphery of which discs the bladesare arranged.

According to the present invention, and as FIG. 3 shows clearly, theseblades have a triangular cross-sec- 3,138,318 Patented June 23, 1964"ice tion having a sharp edge a pointing in the direction of the suctionside (the direction of flow is designated by the arrow f, whilst thearrow r designates the direction of rotation of the mobile blade systemR), so that the ducts delimited by the two neighbouring blades of oneand the same disc are wide open to the molecules which are displaced inthe direction f and do not encounter, in their travel from the upstreamto the downstream sides any arresting transverse surface at any time andwhatever the angular position of the rotor.

Indeed, the transverse surfaces s which form the base of the trianglesare directed downstream and consequently are impinged against only bythe retro-diffusing molecules, which is also advantageous since it mustbe taken into account that retro-diilusion of gases always takes placewhenever there are zones of different molecular density, thisretro-diffusion being elfected from the zone of higher molecular densityto the zone of lower molecular density.

Furthermore, in order to promote the carrying of the molecules towardsthe downstream blades, it is convenient to incline the axis of the ductsof one and the same fixed or mobile disc in the desired direction inaccordance with the direction of rotation of the pump.

In fact, the form and arrangement of the blades thus formed on theperiphery of the discs enable the retrodiiusing molecules to befrequently made to strike against the lateral walls of the ducts andalso the transverse faces s and to be re-despatched, after temporaryabsorption, with a component of speed which tends to send them in thedownstream direction.

In this way, retro-diffusion is reduced and the output and thecompression rate of the pump are increased.

The clearances between the fixed blades and the mobile blades shouldremain small in order that the gases should be always in the molecularcondition.

What is claimed is:

A rotary molecular high-vacuum pump of the kind designed to operate inseries with and upstream of an ordinary vacuum backing pump, comprisinga succession of alternately rotary and stationary blade rings, theblades of each of said rings having a cross-section in the form of anobtuse angle triangle with a sharp rectilinear front edge and a planartransverse rear face in a plane substantially perpendicular to therotation axis, the sharp edges of the blades being circumferentiallyshifted relative to the corresponding planar faces in the direction ofrotation in the case of a rotary blade ring and in the oppositedirection in the case of a stationary blade ring, successive rotary andstationary blade rings being mutually arranged so that the sharp edgesof one blade ring are immediately adjacent the planar faces of the nextpreceding blade ring.

References Cited in the le of this patent UNITED STATES PATENTS 621,030Case et al. Mar. 14, 1899 647,856 Marburg Apr. 17, 1900 853,363Holzwarth May 14, 1907 1,529,925 Say Mar. 17, 1925 2,435,236 ReddingFeb. 3, 1948 2,579,049 Price Dec. 18, 1951 2,738,950 Price Mar. 20, 19562,974,927 Johnson Mar. 14, 1961 FOREIGN PATENTS 626,780 Great BritainJuly 21, 1949 682,418 Great Britain Nov. 12, 1952 418,198 France Sept.21, 1910

